Originally spoken by small groups of people living along the lower Tiber River, Latin spread with the increase of Roman political power, first throughout Italy and then throughout most of western and southern Europe and the central and western Mediterranean coastal regions of Africa. The modern Romance languages developed from the spoken Latin of various parts of the Roman Empire. During the Middle Ages and until comparatively recent times, Latin was the language most widely used in the West for scholarly and literary purposes. Until the latter part of the 20th century its use was required in the liturgy of the Roman Catholic Church.

The oldest example of Latin extant, perhaps dating to the 7th century bce, consists of a four-word inscription in Greek characters on a fibula, or cloak pin. It shows the preservation of full vowels in unstressed syllables—in contrast to the language in later times, which has reduced vowels. Early Latin had a stress accent on the first syllable of a word, in contrast to the Latin of the republican and imperial periods, in which the accent fell on either the next or second to the last syllable of a word.

Latin of the Classical period had six regularly used cases in the declension of nouns and adjectives (nominative, vocative, genitive, dative, accusative, ablative), with traces of a locative case in some declensional classes of nouns. Except for the i-stem and consonant stem declensional classes, which it combines into one group (listed in grammar books as the third declension), Latin kept distinct most of the declensional classes inherited from Indo-European.

During the Classical period there were at least three types of Latin in use: Classical written Latin, Classical oratorical Latin, and the ordinary colloquial Latin used by the average speaker of the language. Spoken Latin continued to change, and it diverged more and more from the Classical norms in grammar, pronunciation, and vocabulary. During the Classical and immediate post-Classical periods, numerous inscriptions provide the major source for spoken Latin, but, after the 3rd century ce, many texts in a popular style, usually called Vulgar Latin, were written. Such writers as St. Jerome and St. Augustine, however, in the late 4th and early 5th centuries, wrote good literary Late Latin.

Subsequent development of Latin continued in two ways. First, the language developed on the basis of local spoken forms and evolved into the modern Romance languages and dialects. Second, the language continued in a more or less standardized form throughout the Middle Ages as the language of religion and scholarship; in this form it had great influence on the development of the West European languages.

Evidence for pronunciation of Classical Latin is often difficult to interpret. Orthography is conventionalized, and grammarians’ comments lack clarity, so that to a considerable extent it is necessary to extrapolate from later developments in Romance in order to describe it.

The most important of the ambiguities bears on Latin intonation and accentuation. The way in which vowels developed in prehistoric Latin suggests the possibility of a stress accent on the first syllable of each word; in later times, however, the accent fell on the penultimate syllable or, when this had “light” quantity, on the antepenultimate. The nature of this accent is hotly disputed: contemporary grammarians seem to suggest it was a musical, tonal accent and not a stress accent. Some scholars claim, however, that Latin grammarians were merely slavishly imitating their Greek counterparts and that the linking of the Latin accent with syllable vowel length makes it unlikely that such an accent was tonal. Probably it was a light stress accent that was normally accompanied by a rise in pitch; in later Latin, evidence suggests that the stress became heavier.

The system of syllable quantity, connected with that of vowel length, must have given Classical Latin distinctive acoustic character. Broadly speaking, a “light” syllable ended in a short vowel and a “heavy” syllable in a long vowel (or diphthong) or a consonant. The distinction must have been reflected to some extent in Late Latin or early Romance, for, even after the system of vowel length was lost, light, or “open,” syllables often developed in a different way from heavy, or “closed,” syllables.

Because the system of vowel length was lost after the Classical period, it is not known with any certainty how vowels were pronounced at that period; but, because of later developments in Romance, the assumption is that the vowel-length distinctions were also associated with qualitative differences, in that short vowels were more open, or lax, than long vowels. Standard orthography did not distinguish between long and short vowels, although in early times various devices were tried to remedy that. At the end of the Roman Republic a so-called apex (one form looked somewhat like a hamza [ ʾ ]) often was used to mark the long vowel, but this mark was replaced in imperial times by an acute accent (′ ). In Classical Latin the length system was an essential feature of verse, even popular verse, and mistakes in vowel length were regarded as barbarous. In later times, however, many poets were obviously unable to conform to the demands of classical prosody and were criticized for allowing accent to override length distinctions.

Besides the long vowels ā, ē, ī, ō, ū and the short vowels ă, ĕ, ĭ, ŏ, ŭ educated speech during the Classical period also used a front rounded vowel, a sound taken from Greek upsilon and pronounced rather like French u (symbolized by y in the International Phonetic Alphabet—IPA) in words borrowed from Greek; in popular speech this was probably pronounced like Latin ŭ, though in later times ī was sometimes substituted. A neutral vowel was probably used in some unaccented syllables and was written u or i (optumus, optimus ‘best’), but the latter rendering became standard. A long ē, from earlier ei, had probably completely merged with ī by the Classical period. Classical pronunciation also used some diphthongs pronounced by educated Romans much as they are spelled, especially ae (earlier ai), pronounced perhaps as an open ē in rustic speech, au (rustic open ō), and oe (earlier oi, Late Latin ē).

The Classical Latin consonant system probably included a series of labial sounds (produced with the lips) /p b m f/ and probably /w/; a dental or alveolar series (produced with the tongue against the front teeth or the alveolar ridge behind the upper front teeth) /t d n s l/ and possibly /r/; a velar series (produced with the tongue approaching or contacting the velum or soft palate) /k g/ and perhaps /ŋ/; and a labiovelar series (pronounced with the lips rounded) /kw gw/. The /k/ sound was written c, and the /kw/ and /gw/ were written qu and gu, respectively.

Of these, /kw/ and /gw/ were probably single labialized velar consonants, not clusters, as they do not make for a heavy syllable; /gw/ occurs only after /n/, so only guesses can be made about its single consonant status. The sound represented by ng (pronounced as in English sing and represented in the IPA by /ŋ/), written ng or gn, may not have had phonemic status (in spite of the pair annus/agnus ‘year’/‘lamb,’ in which /ŋ/ may be regarded as a positional variant of /g/). The Latin letter f probably represented by Classical times a labiodental sound pronounced with the lower lip touching the upper front teeth like its English equivalent, but earlier it may have been a bilabial (pronounced with the two lips touching or approaching one another). The so-called consonantal i and u were probably not true consonants but frictionless semivowels; Romance evidence suggests that they later became a palatalfricative, /j/ (pronounced with the tongue touching or approaching the hard palate and with incomplete closure) and a bilabial fricative, /β/ (pronounced with vibration of the lips and incomplete closure), but there is no suggestion of this during the Classical period. Some Romance scholars suggest that Latin s had a pronunciation like that of z in modern Castilian (with the tip, rather than the blade, raised behind the teeth, giving a lisping impression); in early Latin it was often weakened in final position, a feature that also characterizes eastern Romance languages. The r was probably a tongue trill during the Classical period, but there is earlier evidence that in some positions it may have been a fricative or a flap. There were two sorts of l, velar and palatal (“soft,” when followed by i).

The nasal consonants were probably weakly articulated in some positions, especially medially before s and in final position; probably their medial or final position resulted in mere nasalization of the preceding vowel.

In addition to the consonants shown, educated Roman speakers probably used a series of voiceless aspirated stops, written ph, th, ch, originally borrowed from Greek words but also occurring in native words (pulcher ‘beautiful,’ lachrima ‘tears,’ triumphus ‘triumph,’ etc.) from the end of the 2nd century bce.

Another nonvocalic sound, /h/, was pronounced only by educated speakers even in the Classical period, and references to its loss in vulgar speech are frequent.

Consonants written double in the Classical period were probably so pronounced (a distinction was made, for instance, between anus ‘old woman’ and annus ‘year’). When consonantal i appeared intervocalically, it was always doubled in speech. Before the 2nd century bce, consonant gemination (doubling of sounds) was not shown in orthography but was probably current in speech. The eastern Romance languages, on the whole, retained Latin double consonants (as in Italian), whereas the western languages often simplified them.

Latin reduced the number of Indo-European noun cases from eight to six by incorporating the sociative-instrumental (indicating means or agency) and, apart from isolated forms, the locative (indicating place or place where) into the ablative case (originally indicating the relations of separation and source). The dual number was lost, and a fifth noun declension was developed from a heterogeneous collection of nouns. Probably before the Romance period the number of cases was further reduced (there were two in Old French—nominative, used for the subject of a verb, and oblique, used for all other functions—and Romanian today has two, nominative-accusative, used for the subject and the direct object of a verb, and genitive-dative, used to indicate possession and the indirect object of a verb), and words of the fourth and fifth declension were absorbed into the other three or lost.

Among verb forms, the Indo-European aorist (indicating simple occurrence of an action without reference to duration or completion) and perfect (indicating an action or state completed at the time of utterance or at a time spoken of) combined, and the conjunctive (expressing ideas contrary to fact) and optative (expressing a wish or hope) merged to form the subjunctive mood. New tense forms that developed were the future in -bō and the imperfect in -bam; a passive in -r, also found in Celtic and Tocharian, was also developed. New compound passive tenses were formed with the perfect participle and esse ‘to be’ (e.g., est oneratus ‘he, she, it was burdened’)—such compound tenses developed further in Romance. In general, the morphology of the Classical period was codified and fluctuating forms rigidly fixed. In syntax, too, earlier freedom was restricted; thus, the use of the accusative and infinitive in oratio obliqua (“indirect discourse”) became obligatory, and fine discrimination was required in the use of the subjunctive. Where earlier writers might have used prepositional phrases, Classical authors preferred bare nominal-case forms as terser and more exact. Complex sentences with subtle use of distinctive conjunctions were a feature of the Classical language, and effective play was made with the possibilities offered by flexible word order.

In the post-Classical era, Ciceronian style came to be regarded as laboured and boring, and an epigrammatic compressed style was preferred by such writers as Seneca and Tacitus. Contemporaneously and a little later, florid exuberant writing—often called African—came into fashion, exemplified especially by Apuleius (2nd century ce). Imitation of Classical and post-Classical models continued even into the 6th century, and there seems to have been continuity of literary tradition for some time after the fall of the Western Roman Empire.

The growth of the empire spread Roman culture across much of Europe and North Africa. In all areas, even the outposts, it was not only the rough language of the legions that penetrated but also, it seems, the fine subtleties of Virgilian verse and Ciceronian prose. Research in the late 20th century suggested that in Britain, for instance, Romanization was more widespread and more profound than hitherto suspected and that well-to-do Britons in the colonized region were thoroughly imbued with Roman values. How far these trickled down to the common people is difficult to tell. Because Latin died out in Britain, it is often thought that it had been used only by the elite, but some suggest that it was a result of wholesale slaughter of the Roman British. It is, however, more likely that the pattern of Anglo-Saxon settlements was not in conflict with the Romano-Celtic and that the latter were gradually absorbed into the new society.